CN111522237A - Obstacle avoidance control method for semitrailer - Google Patents

Obstacle avoidance control method for semitrailer Download PDF

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CN111522237A
CN111522237A CN202010335186.1A CN202010335186A CN111522237A CN 111522237 A CN111522237 A CN 111522237A CN 202010335186 A CN202010335186 A CN 202010335186A CN 111522237 A CN111522237 A CN 111522237A
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semitrailer
tractor
trailer
indicating
obstacle
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CN111522237B (en
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孟宇
白国星
李帅
梁晨
荆龙
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University of Science and Technology Beijing USTB
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Nanjing Beike Diyue Technology Co ltd
University of Science and Technology Beijing USTB
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B13/00—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion
    • G05B13/02—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion electric
    • G05B13/04—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion electric involving the use of models or simulators
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/02—Control of position or course in two dimensions
    • G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
    • G05D1/0212—Control of position or course in two dimensions specially adapted to land vehicles with means for defining a desired trajectory
    • G05D1/0214—Control of position or course in two dimensions specially adapted to land vehicles with means for defining a desired trajectory in accordance with safety or protection criteria, e.g. avoiding hazardous areas
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/02—Control of position or course in two dimensions
    • G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
    • G05D1/0231—Control of position or course in two dimensions specially adapted to land vehicles using optical position detecting means
    • G05D1/0238—Control of position or course in two dimensions specially adapted to land vehicles using optical position detecting means using obstacle or wall sensors
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/02—Control of position or course in two dimensions
    • G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
    • G05D1/0257—Control of position or course in two dimensions specially adapted to land vehicles using a radar
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/02—Control of position or course in two dimensions
    • G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
    • G05D1/0268—Control of position or course in two dimensions specially adapted to land vehicles using internal positioning means
    • G05D1/027—Control of position or course in two dimensions specially adapted to land vehicles using internal positioning means comprising intertial navigation means, e.g. azimuth detector

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Abstract

The invention provides an obstacle avoidance control method of a semitrailer, which can enable the semitrailer to accurately track a path and simultaneously avoid obstacles. The method comprises the following steps: establishing a kinematic model of the semitrailer; predicting the pose information of the semitrailer within a period of time in the future according to the established kinematic model; establishing a center line obstacle avoidance model of the semitrailer; according to the predicted pose information and the established center line obstacle avoidance model, an optimization function of nonlinear model prediction control is determined by taking a path tracking error in the control process, controlling output variation and enabling the semitrailer to be far away from the obstacle as targets, and an optimal control sequence of the semitrailer is obtained so that the semitrailer can avoid the obstacle. The invention relates to the field of obstacle avoidance driving control.

Description

Obstacle avoidance control method for semitrailer
Technical Field
The invention relates to the field of obstacle avoidance driving control, in particular to an obstacle avoidance control method for a semitrailer.
Background
The semitrailer consists of a tractor part (as a front body) and a trailer part (as a rear body); the research on semi-trailers is one of the hot spots in the field of vehicles at home and abroad. At present, two main vehicle obstacle avoidance methods are provided, one is a local path planning method, and the other is an obstacle avoidance control method based on Model Predictive Control (MPC). The obstacle avoidance control is to perform various avoidance actions on obstacles in the moving direction of the vehicle, which are obstructed by the outside according to various sensory devices owned by the vehicle, and continue to track a given path after the obstacles are successfully avoided, and the obstacle avoidance control comprises two parts, namely path tracking and obstacle avoidance.
The existing obstacle avoidance control method for the semitrailer is generally based on a kinematic model of a front vehicle body, neglects the track deviation of a rear wheel of a rear vehicle body and causes large tracking error; and due to the special structure of the semitrailer body, although the traditional obstacle avoidance model can ensure that the semitrailer does not collide with obstacles, the passable area of the road surface is greatly reduced, and therefore, a proper semitrailer obstacle avoidance model needs to be constructed.
Disclosure of Invention
The invention aims to provide an obstacle avoidance control method of a semitrailer, and solves the problem that in the prior art, the tracking error is large due to the fact that only a front vehicle body is considered and the track deviation of a rear wheel of a rear trailer is ignored.
In order to solve the technical problem, an embodiment of the present invention provides an obstacle avoidance control method for a semitrailer, including:
establishing a kinematic model of the semitrailer;
predicting the pose information of the semitrailer within a period of time in the future according to the established kinematic model;
establishing a center line obstacle avoidance model of the semitrailer;
according to the predicted pose information and the established center line obstacle avoidance model, an optimization function of nonlinear model prediction control is determined by taking a path tracking error in the control process, controlling output variation and enabling the semitrailer to be far away from the obstacle as targets, and an optimal control sequence of the semitrailer is obtained so that the semitrailer can avoid the obstacle.
Further, the established kinematic model of the semitrailer is represented as:
Figure BDA0002466308140000021
wherein the content of the first and second substances,
Figure BDA0002466308140000022
representing the angular velocity of the course of the tractor; v. offRepresenting the longitudinal travel speed of the tractor; indicating the front wheel steering angle of the tractor; lfbRepresenting the wheelbase of the tractor;
Figure BDA0002466308140000023
representing trailer course angular velocity; gamma represents the angle between the tractor and the trailer; lrbRepresenting the distance between the hinge point and the rear axle of the trailer; thetafRepresenting a tractor heading angle; thetarRepresenting a trailer heading angle;
Figure BDA0002466308140000024
indicating equivalent rear axle L of the tractorfrThe speed component of the midpoint coordinate in the X direction under the global coordinate system (X, Y);
Figure BDA0002466308140000025
indicating equivalent rear axle L of the tractorfrThe velocity component of the midpoint coordinate in the Y direction under the global coordinate system (X, Y);
Figure BDA0002466308140000026
indicating the front end H of the tractorfThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lfaIndicating front axle and front end H of tractorfThe distance between them;
Figure BDA0002466308140000027
indicating the front end H of the tractorfA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
Figure BDA0002466308140000028
indicating tractor rear end TfThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lfcRepresenting the distance between the rear axle and the rear end of the tractor;
Figure BDA0002466308140000029
indicating tractor rear end TfA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
Figure BDA00024663081400000210
indicating front end H of trailerrThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lraIndicating the point of articulation and the front end H of the trailerrThe distance between them;
Figure BDA00024663081400000211
indicating front end H of trailerrA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
Figure BDA00024663081400000212
indicating the rear end T of the trailerrThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lrcRepresenting the distance between the rear axle and the rear end of the trailer;
Figure BDA00024663081400000213
indicating the rear end T of the trailerrThe midpoint is the Y-direction velocity component under the global coordinate system (X, Y).
Further, the predicting the pose information of the semitrailer in a future period according to the established kinematic model comprises:
determining a state quantity x and a control quantity u of a kinematic model of the semitrailer; wherein the state quantity x ═ θfθrγ xfyfxffyffxfryfrxrfyrfxrryrr]TWherein x isfIndicating equivalent rear axle L of the tractorfrThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isfIndicating equivalent rear axle L of the tractorfrThe midpoint is atCoordinates in the Y direction under the global coordinate system (X, Y); x is the number offfIndicating the front end H of the tractorfThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isffIndicating the front end H of the tractorfThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); x is the number offrIndicating tractor rear end TfThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isfrIndicating tractor rear end TfThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); x is the number ofrfIndicating front end H of trailerrThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isrfIndicating front end H of trailerrThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); x is the number ofrrIndicating the rear end T of the trailerrThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isrrIndicating the rear end T of the trailerrThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); control quantity u ═ vf]T；
The relationship between the state quantity x and the control quantity u is described as
Figure BDA0002466308140000031
Wherein the content of the first and second substances,
Figure BDA0002466308140000032
which represents the differential of the state quantity x,
Figure BDA0002466308140000033
represents x, u and
Figure BDA0002466308140000034
the functional relationship of (a);
discretizing the established kinematic model, establishing a prediction model, and predicting a period of time [ t, t + N ] in the future through the prediction model according to the current pose information and the tractor mass center speed information of the semitrailerp]The prediction model is expressed as:
Figure BDA0002466308140000035
wherein T represents aSample period; x (t + i | t) is the state quantity of the ith prediction point at the time t, i is 0,1p(ii) a u (t + m | t) is the control quantity of the mth prediction point at the time t, and m is 0,1p-1；NpTo predict the time domain, NcRepresenting the control time domain.
Further, the establishing of the center line obstacle avoidance model of the semitrailer includes:
determining the jth obstacle in the prediction time domain to the front end H of the tractorfRear end T of tractorfFront end H of trailerrAnd trailer rear end TrThe distances of (a) are respectively:
Figure BDA0002466308140000041
wherein d isffj(t+i|t)、dfrj(t+i|t)、drfj(t+i|t)、drrj(t + i | t) represents the jth obstacle to the front end H of the tractor in the prediction time domainfRear end T of tractorfFront end H of trailerrTrailer rear end TrThe distance of (d); x is the number ofzj、yzjRespectively representing the horizontal coordinate and the vertical coordinate of the jth obstacle;
according to the center line model of the semitrailer and the obtained prediction time domain jth obstacle to the front end H of the tractorfRear end T of tractorfFront end H of trailerrAnd trailer rear end TrWhether the obstacle O is located in the trailer side area B or the trailer side area E:
Figure BDA0002466308140000042
Figure BDA0002466308140000043
wherein B represents a trailer side area, and E represents a trailer side area;
when the jth obstacle is located in the area B or the area E, the vertical distance from the jth obstacle to the center line of the tractor and the center line of the trailer is respectively as follows:
Figure BDA0002466308140000044
wherein d isfj(t+i|t)、drj(t + i | t) represents the vertical distance from the jth obstacle to the center line of the tractor and the center line of the trailer, xfIndicating equivalent front axle L of the trailerrfThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isfIndicating equivalent front axle L of the trailerrfThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y);
and establishing a center line obstacle avoidance model of the semitrailer according to the tractor obstacle avoidance model of the semitrailer, the trailer obstacle avoidance model of the semitrailer and the obtained vertical distance between the jth obstacle and the center line of the tractor and the center line of the trailer.
Further, the centerline model of a semitrailer is represented as:
Figure BDA0002466308140000051
ll＝lr+ls+lb
wherein S iscA centerline model representing the semitrailer; m represents a penalty function term; llRepresenting a minimum safe distance of the obstacle from the centerline of the vehicle body; d3The distance from the center of the outer circle of the obstacle to the center line of the tractor body is represented; o represents an obstacle; II represents the area where the obstacle is located; lrRepresents the circumscribed circle distance of the obstacle; lsRepresents a safety margin; lbRepresenting half the width of the semitrailer body.
Further, the tractor of semitrailer keeps away the barrier model and is:
Figure BDA0002466308140000052
wherein S isfAnd (4) showing a tractor obstacle avoidance model of the semitrailer.
Further, the trailer obstacle avoidance model of the semitrailer is as follows:
Figure BDA0002466308140000053
wherein S isrModel for indicating obstacle avoidance of trailer of semitrailer, d6The distance from the center of the outer circle of the obstacle to the center line of the trailer body is shown.
Further, the established center line obstacle avoidance model of the semitrailer is expressed as:
Figure BDA0002466308140000054
and S (t + i | t) represents an established center line obstacle avoidance model of the semitrailer.
Further, the determined optimization function for the nonlinear model predictive control is represented as:
Figure BDA0002466308140000055
s.t.
Figure BDA0002466308140000056
wherein J represents an optimization function for nonlinear model predictive control, JpAn optimization function representing path tracing, JsRepresents an optimization function for obstacle avoidance control, p represents a weight coefficient, represents a relaxation factor, xfref(t + i | t) represents the state quantity for the ith reference track point at time t, | represents the norm, P, Q, R both represent the weight matrix, s.t. represents the constraint,min、maxrespectively representing the minimum value and the maximum value of the steering angle of the front wheel of the tractor,
Figure BDA0002466308140000061
respectively representing longitudinal acceleration of the tractor
Figure BDA0002466308140000062
The minimum value and the maximum value of (a),
Figure BDA0002466308140000063
respectively representing the steering angular velocity of the front wheels of the tractor
Figure BDA0002466308140000064
Minimum value and maximum value of (d).
Further, an optimal control sequence
Figure BDA0002466308140000065
Wherein the content of the first and second substances,
Figure BDA0002466308140000066
for the 1 st optimal control quantity at the time t, the first element in the optimal control sequence is used
Figure BDA0002466308140000067
The actual control quantity of the semitrailer is used as the actual control quantity of the semitrailer.
The technical scheme of the invention has the following beneficial effects:
in the scheme, a kinematic model of the semitrailer is established; predicting the pose information of the semitrailer within a period of time in the future according to the established kinematic model; establishing a center line obstacle avoidance model of the semitrailer; according to the predicted pose information and the established center line obstacle avoidance model, an optimization function of nonlinear model prediction control is determined by taking a path tracking error in the control process, controlling output variation and enabling the semitrailer to be far away from the obstacle as targets, and an optimal control sequence of the semitrailer is obtained so that the semitrailer can avoid the obstacle. Therefore, by establishing a kinematics model and a center line obstacle avoidance model of the semitrailer consisting of the tractor and the trailer, the semitrailer can accurately track a path and simultaneously complete obstacle avoidance, so that the running safety and reliability of the semitrailer are improved, and the problem of large tracking error caused by the fact that the track deviation of a rear wheel of the trailer is neglected only by considering a front vehicle body in the prior art is solved.
Drawings
Fig. 1 is a sensor installation schematic diagram of an obstacle avoidance control method for a semitrailer according to an embodiment of the present invention;
fig. 2 is a schematic flow chart of an obstacle avoidance control method for a semitrailer according to an embodiment of the present invention;
fig. 3(a) is a schematic diagram of a kinematic model of a semitrailer according to an embodiment of the present invention;
FIG. 3(b) is a schematic view of a towing vehicle provided by an embodiment of the present invention;
FIG. 3(c) is a schematic view of a trailer according to an embodiment of the present invention;
fig. 4 is a schematic diagram of an obstacle avoidance control principle of the semitrailer according to the embodiment of the present invention;
fig. 5 is a detailed flow chart diagram of the obstacle avoidance control method for the semitrailer according to the embodiment of the invention.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.
The invention provides an obstacle avoidance control method of a semitrailer, aiming at the problem of tracking error caused by only considering a front vehicle body and neglecting rear wheel track deviation of a rear trailer in the prior art.
As shown in fig. 1, in order to implement the method for controlling obstacle avoidance of a semitrailer according to this embodiment, a variety of sensors (e.g., a laser radar, an encoder, an inertial navigation system, etc.) need to be installed on the semitrailer, so as to detect pose information and obstacle information of the semitrailer.
As shown in fig. 1, the lidar system includes: 2 laser radars for providing obstacle information; one laser radar is arranged on the left side of the semitrailer and is used for measuring position information of an obstacle on the left side of the semitrailer; another laser radar is installed on the right side of the semitrailer and used for detecting the position information of obstacles on the right side of the semitrailer. In order to ensure the stable work of the laser radar system, the laser radar system is rigidly connected with the semitrailer.
As shown in fig. 1, the encoders may be mounted on the driving wheel shafts on both sides of the semitrailer for measuring the rotating speeds of the driving wheels on both sides, so as to obtain the actual rotating speeds of the wheels.
As shown in fig. 1, the inertial navigation system may include: and the 3 gyroscopes, the 3 accelerometers and the like are respectively used for sensing the angular velocity and the linear acceleration of the semitrailer in three coordinate axis directions, so that information such as the speed, the yaw angle, the position and the like of the semitrailer in a navigation coordinate system can be obtained.
As shown in fig. 2, an obstacle avoidance control method for a semitrailer according to an embodiment of the present invention includes:
s101, establishing a kinematic model of the semitrailer;
s102, predicting the pose information of the semitrailer within a period of time in the future according to the established kinematics model;
s103, establishing a center line obstacle avoidance model of the semitrailer;
and S104, determining an optimization function of nonlinear model predictive control according to the predicted pose information and the established center line obstacle avoidance model and taking the path tracking error, the control output variation and the distance of the semitrailer from the obstacle as targets in the control process as a target, and obtaining an optimal control sequence of the semitrailer so that the semitrailer can avoid the obstacle.
According to the obstacle avoidance control method of the semitrailer, a kinematic model of the semitrailer is established; predicting the pose information of the semitrailer within a period of time in the future according to the established kinematic model; establishing a center line obstacle avoidance model of the semitrailer; according to the predicted pose information and the established center line obstacle avoidance model, an optimization function of nonlinear model prediction control is determined by taking a path tracking error in the control process, controlling output variation and enabling the semitrailer to be far away from the obstacle as targets, and an optimal control sequence of the semitrailer is obtained so that the semitrailer can avoid the obstacle. Therefore, by establishing a kinematics model and a center line obstacle avoidance model of the semitrailer consisting of the tractor and the trailer, the semitrailer can accurately track a path and simultaneously complete obstacle avoidance, so that the running safety and reliability of the semitrailer are improved, and the problem of large tracking error caused by the fact that the track deviation of a rear wheel of the trailer is neglected only by considering a front vehicle body in the prior art is solved.
It should be noted that:
the track deviation of the rear wheel of the rear trailer is a phenomenon of the semitrailer running, the phenomenon is ignored when only a tractor model (a front vehicle body) is built, and the phenomenon is considered when a trailer model (a rear vehicle body) is built/a kinematic model of the semitrailer consisting of the tractor and the trailer is built, so that the phenomenon is closer to the real running condition of the semitrailer.
In this embodiment, in order to execute S102, a kinematic model of the semitrailer needs to be established first, and as shown in fig. 3, the position state of the tractor may be represented as:
Figure BDA0002466308140000081
wherein, as shown in FIG. 3(a),
Figure BDA0002466308140000082
indicating equivalent rear axle L of the tractorfrThe speed component of the midpoint coordinate in the X direction under the global coordinate system (X, Y);
Figure BDA0002466308140000083
indicating equivalent rear axle L of the tractorfrThe velocity component of the midpoint coordinate in the Y direction under the global coordinate system (X, Y);
Figure BDA0002466308140000084
representing the angular velocity of the course of the tractor; v. offRepresenting the longitudinal travel speed of the tractor; indicating the front wheel steering angle of the tractor; lfbRepresenting the wheelbase of the tractor;
the above formula can be simplified as follows:
Figure BDA0002466308140000085
from the geometrical relationships, point P in FIG. 3 can be deducedffAnd point PfrSatisfies the following relation:
Figure BDA0002466308140000086
wherein, as shown in FIG. 3(b), θfRepresenting a tractor heading angle;
Figure BDA0002466308140000087
indicating the front end H of the tractorfThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lfaIndicating front axle and front end H of tractorfThe distance between them;
Figure BDA0002466308140000091
indicating the front end H of the tractorfA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
Figure BDA0002466308140000092
indicating tractor rear end TfThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lfcIndicating tractor rear axle and rear end TfThe distance between them;
Figure BDA0002466308140000093
indicating tractor rear end TfA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
since the tractor and trailer are at P (x)f，yf) The speed of the points is the same and the equivalent rear axle L of the tractorfrAlso assumed to be free of lateral velocity, the relationship can be found:
Figure BDA0002466308140000094
wherein v isrIndicating the longitudinal driving speed, l, of the semitrailerrbRepresenting the distance between the articulation point and the rear axle of the trailer,
Figure BDA0002466308140000095
representing the course angular velocity of the semitrailer, gamma representing the angle between the tractor and the trailer, thetarWhich represents the trailer heading angle, is,
Figure BDA0002466308140000096
indicating equivalent rear axle L of the tractorfrThe velocity component of the midpoint coordinate in the X direction under the global coordinate system (X, Y),
Figure BDA0002466308140000097
indicating equivalent rear axle L of the tractorfrThe velocity component of the midpoint coordinate in the Y direction under the global coordinate system (X, Y);
the complementary equation is γ ═ θf-θrTo obtain the following solution:
Figure BDA0002466308140000098
from the geometric relationship, the point P in FIG. 3(c) can be deducedrfAnd point PrrSatisfies the following relation:
Figure BDA0002466308140000099
wherein the content of the first and second substances,
Figure BDA00024663081400000910
indicating front end H of trailerrThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lraIndicating the point of articulation and the front end H of the trailerrThe distance between them;
Figure BDA00024663081400000911
indicating front end H of trailerrA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
Figure BDA00024663081400000912
indicating the rear end T of the trailerrThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lrcIndicating rear axle and rear end T of trailerrThe distance between them;
Figure BDA00024663081400000913
indicating the rear end T of the trailerrA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
in this embodiment, in summary, the established kinematic model of the semitrailer can be expressed as:
Figure BDA0002466308140000101
wherein the content of the first and second substances,
Figure BDA0002466308140000102
representing the angular velocity of the course of the tractor; v. offRepresenting the longitudinal travel speed of the tractor; indicating the front wheel steering angle of the tractor; lfbRepresenting the wheelbase of the tractor;
Figure BDA0002466308140000103
representing trailer course angular velocity; gamma represents the angle between the tractor and the trailer; lrbRepresenting the distance between the hinge point and the rear axle of the trailer; thetafRepresenting a tractor heading angle; thetarRepresenting a trailer heading angle;
Figure BDA0002466308140000104
indicating equivalent rear axle L of the tractorfrThe speed component of the midpoint coordinate in the X direction under the global coordinate system (X, Y);
Figure BDA0002466308140000105
indicating equivalent rear axle L of the tractorfrThe velocity component of the midpoint coordinate in the Y direction under the global coordinate system (X, Y);
Figure BDA0002466308140000106
indicating the front end H of the tractorfThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lfaIndicating front axle and front end H of tractorfThe distance between them;
Figure BDA0002466308140000107
indicating the front end H of the tractorfA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
Figure BDA0002466308140000108
indicating tractor rear end TfSpeed of midpoint in X direction under global coordinate system (X, Y)An amount; lfcIndicating tractor rear axle and rear end TfThe distance between them;
Figure BDA0002466308140000109
indicating tractor rear end TfA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
Figure BDA00024663081400001010
indicating front end H of trailerrThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lraIndicating the point of articulation and the front end H of the trailerrThe distance between them;
Figure BDA00024663081400001011
indicating front end H of trailerrA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
Figure BDA00024663081400001012
indicating the rear end T of the trailerrThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lrcRepresenting the distance between the rear axle and the rear end of the trailer;
Figure BDA00024663081400001013
indicating the rear end T of the trailerrThe midpoint is the Y-direction velocity component under the global coordinate system (X, Y).
In a specific implementation manner of the foregoing obstacle avoidance control method for a semitrailer, further, the predicting pose information of the semitrailer within a future period of time according to the established kinematic model includes:
determining a state quantity x and a control quantity u of a kinematic model of the semitrailer; wherein the state quantity x ═ θfθrγ xfyfxffyffxfryfrxrfyrfxrryrr]TWherein x isfIndicating equivalent rear axle L of the tractorfrThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isfIndicating equivalent rear axle L of the tractorfrThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); x is the number offfTo representFront end H of tractorfThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isffIndicating the front end H of the tractorfThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); x is the number offrIndicating tractor rear end TfThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isfrIndicating tractor rear end TfThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); x is the number ofrfIndicating front end H of trailerrThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isrfIndicating front end H of trailerrThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); x is the number ofrrIndicating the rear end T of the trailerrThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isrrIndicating the rear end T of the trailerrThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); control quantity u ═ vf]T；
The relationship between the state quantity x and the control quantity u is described as
Figure BDA0002466308140000111
Wherein the content of the first and second substances,
Figure BDA0002466308140000112
which represents the differential of the state quantity x,
Figure BDA0002466308140000113
represents x, u and
Figure BDA0002466308140000114
the functional relationship of (a);
discretizing the established kinematic model, establishing a prediction model, and predicting a period of time [ t, t + N ] in the future through the prediction model according to the current pose information (the pose information comprises a position and a course angle) of the semitrailer and the speed information of the mass center (the mass center is short for the mass center)p]The prediction model is expressed as:
Figure BDA0002466308140000115
wherein T represents a sampling period; x (t + i | t) is the state quantity of the ith prediction point at the time t, i is 0,1p(ii) a u (t + m | t) is the control quantity of the mth prediction point at the time t, and m is 0,1p-1；NpTo predict the time domain, NcRepresenting the control time domain.
In this embodiment, when the prediction model is established, the kinematic model of the semitrailer needs to be discretized first, and then the kinematic model is rewritten into an iterative equation by using a single-step eulerian method, and the state quantity at the next moment can be predicted by using the current state quantity through the iterative equation.
In a specific implementation manner of the foregoing obstacle avoidance control method for the semitrailer, further, the establishing a center line obstacle avoidance model of the semitrailer includes:
determining the jth obstacle in the prediction time domain to the front end H of the tractorfRear end T of tractorfFront end H of trailerrAnd trailer rear end TrThe distances of (a) are respectively:
Figure BDA0002466308140000121
wherein d isffj(t+i|t)、dfrj(t+i|t)、drfj(t+i|t)、drri(t + i | t) represents the jth obstacle to the front end H of the tractor in the prediction time domainfRear end T of tractorfFront end H of trailerrTrailer rear end TrThe distance of (d); x is the number ofzj、yzjRespectively representing the horizontal coordinate and the vertical coordinate of the jth obstacle;
according to the center line model of the semitrailer and the obtained prediction time domain jth obstacle to the front end H of the tractorfRear end T of tractorfFront end H of trailerrAnd trailer rear end TrCan determine whether the obstacle is located in the area B or E as shown in fig. 3(B) and (c):
Figure BDA0002466308140000122
Figure BDA0002466308140000123
wherein B represents a trailer side area, and E represents a trailer side area;
when the jth barrier is located in the area B or the area E, the vertical distances from the jth barrier to the centerline of the tractor and the centerline of the trailer are respectively as follows:
Figure BDA0002466308140000124
wherein d isfj(t+i|t)、drj(t + i | t) represents the vertical distance from the jth obstacle to the center line of the tractor and the center line of the trailer, xfIndicating equivalent front axle L of the trailerrfThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isfIndicating equivalent front axle L of the trailerrfThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y);
and establishing a center line obstacle avoidance model of the semitrailer according to the tractor obstacle avoidance model of the semitrailer, the trailer obstacle avoidance model of the semitrailer and the obtained vertical distance between the jth obstacle and the center line of the tractor and the center line of the trailer.
In a specific embodiment of the foregoing obstacle avoidance control method for a semitrailer, further, a centerline model of the semitrailer is represented as:
Figure BDA0002466308140000131
ll＝lr+ls+lb
wherein S iscA centerline model representing the semitrailer; m represents a penalty function term; llRepresenting a minimum safe distance of the obstacle from the centerline of the vehicle body; d3The distance from the center of the outer circle of the obstacle to the center line of the tractor body is represented; o represents an obstacle; II represents the area where the obstacle is located; lrRepresents the circumscribed circle distance of the obstacle; lsRepresents a safety margin; lbIndicating the width of the semitrailer bodyHalf of that.
In this embodiment, M is a penalty function term, and it is desirable that the vehicle can react quickly when the distance from the obstacle to the vehicle body is less than the minimum safe distance. Assuming that the distance is only less than the minimum safe distance of 1cm, under the action of the optimization function, the vehicle may tend to move away from the obstacle, but after all, the value is too small, the influence on the driving direction is not particularly obvious compared with the weight influence of the transverse and longitudinal errors of the vehicle, and the vehicle may preferentially consider moving towards the direction with smaller transverse and longitudinal errors and further approach the obstacle. Therefore, M plays the role of amplifying the value as much as possible, and the value of M can be 10^7 in the experimental process.
In a specific implementation manner of the above-mentioned obstacle avoidance control method for the semitrailer, further, the tractor obstacle avoidance model of the semitrailer is:
Figure BDA0002466308140000132
wherein S isfAnd (4) showing a tractor obstacle avoidance model of the semitrailer.
In a specific implementation manner of the obstacle avoidance control method for the semitrailer, further, a trailer obstacle avoidance model of the semitrailer is as follows:
Figure BDA0002466308140000133
wherein S isrModel for indicating obstacle avoidance of trailer of semitrailer, d6The distance from the center of the outer circle of the obstacle to the center line of the trailer body is shown.
In a specific implementation manner of the foregoing obstacle avoidance control method for a semitrailer, further, the established center line obstacle avoidance model of the semitrailer is represented as:
Figure BDA0002466308140000141
and S (t + i | t) represents an established center line obstacle avoidance model of the semitrailer.
As shown in fig. 4 and 5, the position and the obstacle information can be collected by using sensors such as an inertial navigation system and a laser radar, and then, according to the model prediction control theory, a Nonlinear Model Prediction Controller (NMPC) is combined with the current sensor measurement value and the prediction model of the semitrailer to predict a period of time [ t, t + N ] in the future of the semitrailerp]Inner pose output, where time length NpNamely, the prediction time domain; determining an optimization function of the nonlinear model predictive control according to the predicted pose output, the reference track and the established center line obstacle avoidance model of the semitrailer, and then solving the optimization function in a rolling way to obtain the [ t, t + N ] in a period of time in the futurec]In which the time length NcReferred to as the control time domain; then the first controlled variable element of the control sequence is input into the semitrailer as an actual controlled variable.
In this embodiment, for obstacle avoidance control of a semitrailer, the optimization target includes 2 aspects of path tracking and obstacle avoidance control:
1) in the process of realizing the path tracking of the semitrailer, in order to ensure that the semitrailer accurately tracks the expected path, a path tracking optimization function needs to punish the sum of pose deviations in a prediction time domain, wherein the pose of the semitrailer comprises the abscissa, the ordinate and a course angle of the semitrailer in a global coordinate system; because the control quantity increment of semitrailer influences the stability that the semitrailer travel, the too big messenger's semitrailer accelerates suddenly or decelerates suddenly in the control quantity change in unit time, seriously influences its normal driving, so in order to guarantee that the semitrailer turns to level and motion stability, the sum of the semitrailer control quantity increment in the prediction time domain needs punishment to the path tracking optimization function, consequently sets up the path tracking optimization function and is:
Figure BDA0002466308140000142
wherein, JpAn optimization function representing path tracking, p representing a weight coefficient, representing a relaxation factor, xfref(t + i | t) represents the state quantity of the ith reference track point at time t, | represents the norm, P, Q, R both representA weight matrix;
2) because the semitrailer needs to realize the function of avoiding the barrier, need guarantee feasible traffic area as far as possible simultaneously, consequently set up and keep away barrier control optimization function and do:
Figure BDA0002466308140000151
wherein, JsAn optimization function representing obstacle avoidance control;
in the present embodiment, the first and second electrodes are,
Figure BDA0002466308140000152
the meanings of (A) are as follows:
this value is extremely large when the obstacle is within the obstacle range set by the semitrailer; when the obstacle is not in the obstacle range set by the semitrailer, the value is 0; by setting this value as the optimization target, it is possible to reversely generate the control amount for moving the vehicle away from the obstacle.
By combining the above 2 cases, the optimization function of the nonlinear model predictive control is:
Figure BDA0002466308140000153
finally, constraints of the optimization function need to be determined.
In this embodiment, the turning angle of the steering wheel of the semitrailer has a certain range, that is to saymin<<maxWherein, the front wheel steering angle of the tractor is shown.
In order to make the semitrailer drive as smoothly as possible, time domain constraint conditions need to be met
Figure BDA0002466308140000154
Wherein the content of the first and second substances,
Figure BDA0002466308140000155
which is indicative of the longitudinal acceleration of the tractor,
Figure BDA0002466308140000156
indicating the steering angular velocity of the front wheels of the tractor.
In combination with the optimization function and constraints in the above equation, the optimization function for the nonlinear model predictive control can be expressed in the form:
Figure BDA0002466308140000157
s.t.
Figure BDA0002466308140000158
in this embodiment, the path tracking is to solve the constrained optimization problem in each sampling time, and by solving the problem, if there is no optimal solution, the optimal solution is solved again, and if there is an optimal solution, the optimal control sequence can be obtained
Figure BDA0002466308140000161
Figure BDA0002466308140000162
For the 1 st optimal control quantity at the time t, the first element in the control sequence is used
Figure BDA0002466308140000163
The actual control input quantity of the semitrailer is transmitted to the semitrailer platform to track a desired path. In the next control period, the NMPC solves the optimization problem again with the next moment as an initial state, and then takes the first element in the control sequence of the solution result as the actual control quantity of the semitrailer, and the optimization is executed in sequence in a circulating and reciprocating manner according to the basic principle of the NMPC;
the controlled semitrailer controls according to the control quantity given by the NMPC
Figure BDA0002466308140000164
The driving wheel rotates according to the corresponding rotating speed, so that the current rotating speed of the driving wheel of the controlled semitrailer is consistent with the rotating speed of the expected driving wheel, and the path tracking and obstacle avoidance of the semitrailer are realized.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (10)

1. An obstacle avoidance control method of a semitrailer is characterized by comprising the following steps:
establishing a kinematic model of the semitrailer;
predicting the pose information of the semitrailer within a period of time in the future according to the established kinematic model;
establishing a center line obstacle avoidance model of the semitrailer;
according to the predicted pose information and the established center line obstacle avoidance model, an optimization function of nonlinear model prediction control is determined by taking a path tracking error in the control process, controlling output variation and enabling the semitrailer to be far away from the obstacle as targets, and an optimal control sequence of the semitrailer is obtained so that the semitrailer can avoid the obstacle.
2. The obstacle avoidance control method for the semitrailer according to claim 1, wherein the established kinematic model of the semitrailer is represented as:
Figure FDA0002466308130000011
wherein the content of the first and second substances,
Figure FDA0002466308130000012
representing the angular velocity of the course of the tractor; v. offRepresenting the longitudinal travel speed of the tractor; indicating the front wheel steering angle of the tractor; lfbRepresenting the wheelbase of the tractor;
Figure FDA0002466308130000013
representing trailer course angular velocity; gamma represents the angle between the tractor and the trailer; lrbRepresenting the distance between the hinge point and the rear axle of the trailer; thetafTo representA tractor course angle; thetarRepresenting a trailer heading angle;
Figure FDA0002466308130000014
indicating equivalent rear axle L of the tractorfrThe speed component of the midpoint coordinate in the X direction under the global coordinate system (X, Y);
Figure FDA0002466308130000015
indicating equivalent rear axle L of the tractorfrThe velocity component of the midpoint coordinate in the Y direction under the global coordinate system (X, Y);
Figure FDA0002466308130000016
indicating the front end H of the tractorfThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lfaIndicating front axle and front end H of tractorfThe distance between them;
Figure FDA0002466308130000021
indicating the front end H of the tractorfA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
Figure FDA0002466308130000022
indicating tractor rear end TfThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lfcRepresenting the distance between the rear axle and the rear end of the tractor;
Figure FDA0002466308130000023
indicating tractor rear end TfA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
Figure FDA0002466308130000024
indicating front end H of trailerrThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lraIndicating the point of articulation and the front end H of the trailerrThe distance between them;
Figure FDA0002466308130000025
indicating front end H of trailerrA Y-direction velocity component of the midpoint under the global coordinate system (X, Y);
Figure FDA0002466308130000026
indicating the rear end T of the trailerrThe velocity component of the midpoint in the X direction under the global coordinate system (X, Y); lrcRepresenting the distance between the rear axle and the rear end of the trailer;
Figure FDA0002466308130000027
indicating the rear end T of the trailerrThe midpoint is the Y-direction velocity component under the global coordinate system (X, Y).
3. The obstacle avoidance control method of the semitrailer of claim 2, wherein the predicting the pose information of the semitrailer within a future period of time according to the established kinematic model comprises:
determining a state quantity x and a control quantity u of a kinematic model of the semitrailer; wherein the state quantity x ═ θfθrγ xfyfxffyffxfryfrxrfyrfxrryrr]TWherein x isfIndicating equivalent rear axle L of the tractorfrThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isfIndicating equivalent rear axle L of the tractorfrThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); x is the number offfIndicating the front end H of the tractorfThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isffIndicating the front end H of the tractorfThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); x is the number offrIndicating tractor rear end TfThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isfrIndicating tractor rear end TfThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); x is the number ofrfIndicating front end H of trailerrThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isrfIndicating front end H of trailerrThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); x is the number ofrrIndicating the rear end T of the trailerrThe coordinate of the midpoint in the X direction under the global coordinate system (X, Y); y isrrIndicating the rear end T of the trailerrThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y); control quantity u ═ vf]T；
The relationship between the state quantity x and the control quantity u is described as
Figure FDA0002466308130000028
Wherein the content of the first and second substances,
Figure FDA0002466308130000029
which represents the differential of the state quantity x,
Figure FDA00024663081300000210
represents x, u and
Figure FDA00024663081300000211
the functional relationship of (a);
discretizing the established kinematic model, establishing a prediction model, and predicting a period of time [ t, t + N ] in the future through the prediction model according to the current pose information and the tractor mass center speed information of the semitrailerp]The prediction model is expressed as:
Figure FDA0002466308130000031
wherein T represents a sampling period; x (t + i | t) is the state quantity of the ith prediction point at the time t, i is 0,1p(ii) a u (t + m | t) is the control quantity of the mth prediction point at the time t, and m is 0,1p-1；NpTo predict the time domain, NcRepresenting the control time domain.
4. The obstacle avoidance control method for the semitrailer according to claim 3, wherein the establishing of the center line obstacle avoidance model for the semitrailer comprises:
determining the jth obstacle in the prediction time domain to the front end H of the tractorfRear end T of tractorfFront end H of trailerrAnd trailer rear end TrThe distances of (a) are respectively:
Figure FDA0002466308130000032
wherein d isffj(t+i|t)、dfrj(t+i|t)、drfj(t+i|t)、drrj(t + i | t) represents the jth obstacle to the front end H of the tractor in the prediction time domainfRear end T of tractorfFront end H of trailerrTrailer rear end TrThe distance of (d); x is the number ofzj、yzjRespectively representing the horizontal coordinate and the vertical coordinate of the jth obstacle;
according to the center line model of the semitrailer and the obtained prediction time domain jth obstacle to the front end H of the tractorfRear end T of tractorfFront end H of trailerrAnd trailer rear end TrWhether the obstacle O is located in the trailer side area B or the trailer side area E:
Figure FDA0002466308130000033
Figure FDA0002466308130000034
wherein B represents a trailer side area, and E represents a trailer side area;
when the jth obstacle is located in the area B or the area E, the vertical distance from the jth obstacle to the center line of the tractor and the center line of the trailer is respectively as follows:
Figure FDA0002466308130000041
wherein d isfj(t+i|t)、drj(t + i | t) represents the vertical distance from the jth obstacle to the center line of the tractor and the center line of the trailer, xfIndicating equivalent front axle L of the trailerrfThe midpoint being below the global coordinate system (X, Y) by XA directional coordinate; y isfIndicating equivalent front axle L of the trailerrfThe coordinate of the midpoint in the Y direction under the global coordinate system (X, Y);
and establishing a center line obstacle avoidance model of the semitrailer according to the tractor obstacle avoidance model of the semitrailer, the trailer obstacle avoidance model of the semitrailer and the obtained vertical distance between the jth obstacle and the center line of the tractor and the center line of the trailer.
5. The obstacle avoidance control method for the semitrailer according to claim 4, wherein the centerline model of the semitrailer is represented as:
Figure FDA0002466308130000042
ll＝lr+ls+lb
wherein S iscA centerline model representing the semitrailer; m represents a penalty function term; llRepresenting a minimum safe distance of the obstacle from the centerline of the vehicle body; d3The distance from the center of the outer circle of the obstacle to the center line of the tractor body is represented; o represents an obstacle; II represents the area where the obstacle is located; lrRepresents the circumscribed circle distance of the obstacle; lsRepresents a safety margin; lbRepresenting half the width of the semitrailer body.
6. The obstacle avoidance control method of the semitrailer according to claim 5, wherein the tractor obstacle avoidance model of the semitrailer is:
Figure FDA0002466308130000043
wherein S isfAnd (4) showing a tractor obstacle avoidance model of the semitrailer.
7. The obstacle avoidance control method of the semitrailer according to claim 6, wherein the obstacle avoidance model of the semitrailer is:
Figure FDA0002466308130000044
wherein S isrModel for indicating obstacle avoidance of trailer of semitrailer, d6The distance from the center of the outer circle of the obstacle to the center line of the trailer body is shown.
8. The obstacle avoidance control method for the semitrailer according to claim 7, wherein the established center line obstacle avoidance model of the semitrailer is represented as:
Figure FDA0002466308130000051
wherein s (t + i | t) represents the established center line obstacle avoidance model of the semitrailer.
9. The obstacle avoidance control method for the semitrailer according to claim 8, characterized in that the determined optimization function of the nonlinear model predictive control is expressed as:
Figure FDA0002466308130000052
s.t.
Figure FDA0002466308130000053
wherein J represents an optimization function for nonlinear model predictive control, JpAn optimization function representing path tracing, JsRepresents an optimization function for obstacle avoidance control, p represents a weight coefficient, represents a relaxation factor, xfref(t + i | t) represents the state quantity of the ith reference track point at the time t, | | · | | represents a norm, P, Q, R represents a weight matrix, s.t. represents a constraint condition,min、maxrespectively representing the minimum value and the maximum value of the steering angle of the front wheel of the tractor,
Figure FDA0002466308130000054
respectively show the tractorLongitudinal acceleration of vehicle
Figure FDA0002466308130000055
The minimum value and the maximum value of (a),
Figure FDA0002466308130000056
respectively representing the steering angular velocity of the front wheels of the tractor
Figure FDA0002466308130000057
Minimum value and maximum value of (d).
10. An obstacle avoidance control method for a semitrailer according to claim 9, characterised in that the optimal control sequence
Figure FDA0002466308130000058
Wherein the content of the first and second substances,
Figure FDA0002466308130000059
for the 1 st optimal control quantity at the time t, the first element in the optimal control sequence is used
Figure FDA00024663081300000510
The actual control quantity of the semitrailer is used as the actual control quantity of the semitrailer.
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CN114003030B (en) * 2021-10-09 2023-08-08 北京科技大学 Path tracking control method of two-wheel differential mobile robot considering centroid change

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